Wear and corrosion resistance of Nb-V carbide layers produced in vermicular cast iron using TRD treatments

• Published in: Surface & coatings technology 2020-09, Vol.397, p.126050, Article 126050
• Main Authors: Mariani, Fábio Edson, Takeya, Gustavo Satoru, Lombardi, Amadeu Neto, Picone, Carlos Alberto, Casteletti, Luiz Carlos
• Format: Article
• Language: English
• Subjects: Aluminum; Austempering; Carbides; Cast iron; Corrosion; Corrosion resistance; Corrosion tests; Corrosive wear; Diamond pyramid hardness; Diffusion layers; Molten salts; Niobium; Optical microscopy; Salt baths; Sodium borates; Substrates; Thickness; TRD treatment; Vermicular cast iron; Wear; Wear resistance
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2020.126050

Nb, V and Nb-V carbide layers were produced by means of the diffusion thermo-reactive treatment (TRD) in a vermicular cast iron, in baths composed of sodium borate, aluminum, ferro‑niobium and/or ferro‑vanadium, at 1000 °C with 2 h treatment time. Austempering was carried out after the TRD treatment in a molten salt bath at 300 °C. The samples were characterized by optical microscopy, XRD, Vickers microhardness, Daimler-Benz Rockwell-C, microadhesive wear tests and corrosion tests using potentiodynamic polarization tests. The TRD treatments were highly efficient in the production of uniform carbide layers, with thicknesses above 25 μm and with good adhesions to the substrates. The layers showed hardness above 2300, 2500 and 3050 HV for the cases of Nb, V and Nb-V carbides, respectively. The wear resistance of the samples was increased from 10 to 30× in relation to the austempered substrate. The layers also showed corrosion resistance much higher than that of the substrate. The results obtained indicated the great effectiveness of the TRD treatment for the production of high performance carbide layers in vermicular cast iron. [Display omitted] •The TRD treatments were highly efficient for the production of carbide layers in the studied vermicular cast iron.•These layers showed thicknesses greater than 25 µm, uniformity and with good adhesions to the substrates.•The layers showed hardness above 2300, 2500 and 3050 HV for the cases of Nb, V and Nb-V carbides, respectively.•The wear resistance was increased from 10x (layers of NbC) up to 30x (layers of NbVC2 and VC) in relation to the substrate.•All layers showed corrosion resistance much higher than that of the substrates.